One well-known method for the exposure of photographic photosensitive elements is an image forming method of the scanner system comprising the steps of scanning an original to produce image signals, subjecting a photographic silver halide photosensitive element to exposure in accordance with the image signals, and forming a negative or positive image corresponding to the image of the original.
There is a desire to have a procedure of providing outputs of a scanner to a film and directly printing on a printing plate without a transfer step as well as a scanner photosensitive element having ultrahigh contrast with respect to a scanner light source having a soft beam profile.
There are known a number of photosensitive elements having a photosensitive layer on a support wherein images are formed by imagewise exposure. Among these, a technique of forming images through heat development is known as a system capable of simplifying image forming means and contributing to the environmental protection.
From the contemporary standpoints of environmental protection and space saving, it is strongly desired in the photomechanical process field to reduce the quantity of spent solution. Needed in this regard is a technology relating to photothermographic elements for use in reprophotography which can be effectively exposed by means of laser scanners or laser image setters and produce distinct black images having high resolution and sharpness. These photothermographic elements offer to the customer a simple thermographic system which eliminates a need for solution type chemical agents and is not detrimental to the environment.
The technology of forming images through heat development is disclosed, for example, in U.S. Pat. Nos. 3,152,904 and 3,457,075, D. Morgan and B. Shely, "Thermally Processed Silver Systems" in "Imaging Processes and Materials," Neblette, 8th Ed., Sturge, V. Walworth and A. Shepp Ed., page 2, 1969. These photothermographic elements generally contain a reducible non-photosensitive silver source (e.g., organic silver salt), a catalytic amount of a photocatalyst (e.g., silver halide), and a reducing agent for silver, typically dispersed in an organic binder matrix. Photothermographic elements are stable at room temperature. When they are heated at an elevated temperature (e.g., 80.degree. C. or higher) after exposure, redox reaction takes place between the reducible silver source (functioning as an oxidizing agent) and the reducing agent to form silver. This redox reaction is promoted by the catalysis of a latent image produced by exposure. Silver formed by reaction of the reducible silver salt in exposed regions provides black images in contrast to unexposed regions, forming an image.
Photothermographic elements of this type are well known in the art. In most of these elements, photosensitive layers are formed by applying coating solutions based on organic solvents such as toluene, methyl ethyl ketone (MEK) and methanol, followed by drying. The use of organic solvents is not only harmful to workers in the manufacturing procedure, but disadvantageous because of the cost for recovery and disposal of the solvents.
It is contemplated to form photosensitive layers using coating solutions based on water solvent which eliminates such concern. Such photosensitive layers are sometimes referred to as "aqueous photosensitive layers," hereinafter. For example, JP-A 52626/1974 and 116144/1978 disclose the use of gelatin as the binder. JP-A 151138/1975 discloses polyvinyl alcohol as the binder. Further, JP-A 61747/1985 discloses a combined use of gelatin and polyvinyl alcohol. Besides, JP-A 28737/1983 discloses a photosensitive layer containing water-soluble polyvinyl acetal as the binder.
It is true that the use of these binders has great environmental and economical advantages in that photosensitive layers can be formed using coating solutions based on water solvent.
However, the use of such polymers as gelatin, polyvinyl alcohol and water-soluble polyacetal as the binder results in photosensitive materials which are of extremely low commodity worth in that a coating whose surface quality is practically acceptable is not available since these polymers are less compatible with the organic silver salt, that the silver tone of developed areas becomes brown or yellow and far from the essentially favorable black and that exposed areas have a low blackened density and unexposed areas have a high density.
There is a desire to develop a photothermographic element or aqueous photosensitive element having environmental and economic benefits, good coating surface quality, acceptable silver tone and satisfactory photographic properties (especially high Dmax) upon development.
In general, photothermographic elements undergo dimensional shrinkage or expansion during heat development. Such dimensional changes give rise to a serious problem against precise multi-color printing when the film is used as a photographic printing plate. The dimensional changes also cause variations in image density and seriously affect so especially in the case of fine images like photographic printing halftone images. Improvements in these problems associated with heat development are desired.
In order that photothermographic material produce an image faithful to exposure and having high resolution, it is effective to add an anti-irradiation dye or provide an anti-halation layer like the conventional wet system photographic silver halide photosensitive material. The anti-irradiation dye is mainly added to the photosensitive layer while the anti-halation layer is disposed between the support and the photosensitive layer or on that side of the support remote from the photosensitive layer. For example, where an output of a near infrared laser is to be recorded, a dye having absorption in the infrared region is necessary. Exemplary infrared dyes include indolenine cyanine dyes as described in JP-A 182640/1992 and dihydroperimidine squarylium dyes having squaric acid bonded to a dihydroperimidine nucleus at its para-position as described in U.S. Pat. No. 5,380,635.
U.S. Pat. No. 5,545,515 describes a photothermographic material comprising a hydrazine derivative of specific structure. It is also disclosed that an indolenine cyanine dye is added to an anti-halation or back layer. However, there is not available a dye which can prevent irradiation within the photosensitive layer or prevent halation between the photosensitive layer and the support. To produce an ultrahigh contrast image faithful to exposure, an anti-irradiation or anti-halation dye having no influence on image formation within the photosensitive layer is needed. Even in the anti-halation layer on the back side, some dyes give rise to the problem of residual color or resolution decline.